The present invention relates to a method for manufacturing a wall structure. The method is particularly directed to manufacturing a wall structure, which is capable of withstanding a high thermal load, and especially to an engine wall structure. The method is specifically directed to manufacturing the wall structure of a thrust chamber (a combustion chamber and/or an outlet nozzle) for use in a rocket engine. The invention is further directed to a machining tool configured for being used in a step in the manufacturing method.
During operation, a rocket nozzle is subjected to very high stresses, for example in the form of a very high temperature on its inside (in the magnitude of 800° K.) and a very low temperature on its outside (in the magnitude of 50° K.). As a result of this high thermal load, stringent requirements are placed upon the choice of material, design and manufacture of the outlet nozzle. At least there is a need for effective cooling of the outlet nozzle.
The wall structure forming the outlet nozzle has a tubular shape with a varying diameter along a centre axis. More specifically, the outlet nozzle wall structure has a conical or parabolic shape. The outlet nozzle normally has a diameter ratio from the aft or large outlet end to the forward or small inlet end in the interval from 2:1 to 4:1.
The outlet nozzle wall structure comprises cooling channels extending between an upstream end and a downstream end of the nozzle. According to one previously known design, the outlet nozzle wall structure comprises an inner wall, to which hot gas is admitted during engine operation and an outer wall, which is colder than the inner wall during engine operation. There is a plurality of elongated webs connecting the inner wall to the outer wall dividing the space between the walls into a plurality of cooling channels.
During engine operation, any cooling medium may be used to flow through the cooling channels. Regarding a rocket engine, the rocket engine fuel is normally used as a cooling medium in the outlet nozzle. The rocket engine may be driven with hydrogen or a hydrocarbon, i.e. kerosene, as a fuel. Thus, the fuel is introduced in a cold state into the wall structure, delivered through the cooling channels while absorbing heat via the inner wall and is subsequently used to generate the thrust. Heat is transferred from the hot gases to the inner wall, further on to the fuel, from the fuel to the outer wall, and, finally, from the outer wall to any medium surrounding it. Heat is also transported away by the coolant as the coolant temperature increases by the cooling. The hot gases may comprise a flame generated by a combustion of gases and/or fuel.
According to a known method, for manufacturing the outlet nozzle, in a first step, a first machining tool (a turning lathe) is used for working an external surface of the workpiece in order to achieve a desired workpiece thickness. In a second step, a second machining tool (a milling cutter) with two spaced rotary machining elements in the form of cutting wheels is used. The cutting wheels are arranged at a mutual distance corresponding to a desired web thickness. The milling cutter is fed across an external surface of a cylindrical workpiece forming two groves and an intermediate web. The cutting wheels work on the side surfaces of the web.
The milling cutter is indexed in the circumferential direction of the workpiece and run, wherein a plurality of webs are produced. Thus, the webs are integrated in and project from an inner wall. Subsequently, an outer wall is positioned around the inner wall, and joined to the edges of the webs by welding.
It is desirable to provide a method for manufacturing a wall structure provided with cooling channels which extend in a diverging manner, which creates conditions for a faster operation, and robustly achieved channel height, than previously known methods. The invention is especially directed at manufacturing a tubular wall structure with an increasing diameter with axial position and particularly suited for a rocket engine member.
According to an aspect of the present invention, a method comprises the steps of producing at least one elongated web in a workpiece by feeding a machining tool along the workpiece, wherein the machining tool simultaneously machines a first side surface of the web, a second side surface of the web and a top surface of the web.
In this way, all three surfaces (side surfaces and top surface) of the web are worked in one single run. The height, which is very important for the cooling performance, of the web is determined by the position of an intermediate machining element in the machining tool. Thus, the first turning step according to prior art may be dispensed with.
Further, prior art problems relating to grindings sticking between the two cutting wheels are decreased or prevented. All in all, a more reliable manufacturing process is achieved.
It is also desirable to provide a machining tool adapted for manufacturing a wall structure provided with cooling channels, which creates conditions for a faster operation than previously known methods.
According to another aspect of the present invention, a machining tool comprises a first rotary cutting element and a second rotary cutting element, wherein the first and second rotary cutting elements are positioned at a distance from each other, wherein the machining tool comprises, a third rotary cutting element arranged between the first and second rotary cutting elements.
Further preferred embodiments and advantages will be apparent from the following description and drawings.